Over the last decade, the increased worldwide demand for electrical power has increased the number of land-based gas turbine systems. One of the expensive components in a gas turbine system is a transition duct in which the actual hot gas is ducted from the exit of the combustion chamber to the inlet of the turbine. The transition duct includes a ceramic layer and a metallic bonding layer for thermal and corrosion protection. The flow of hot gas degrades a ceramic coating or layer on the inner wall of the transition duct, and consequently, after using the transition duct up to its operating limit, the transition duct must be periodically refurbished to replace the degraded ceramic layer.
Prior to replacing the ceramic layer, however, the ceramic layer must be completely removed in order to ensure that the new ceramic layer is reliably adhered onto the inner wall of the transition duct. This removal process typically includes a grit blasting technique or a water jet cleaning technique that physically or mechanically removes the ceramic layer from the inner walls and may, in some instances, include a combination of mechanical and chemical methods. The metallic bonding layer is subsequently removed either by a physical or mechanical process using one or more of the aforementioned techniques or by a chemical process using intimate chemical exposure.
In addition to the expensive and labor intensive nature of the grit blasting process, the extreme imprecision of the grit blasting technique causes numerous problems during the refurbishing process. For example, the grit blasting technique not only removes the metallic bonding layer and the ceramic layer, but also often reduces the thickness of the base material for the walls of the transition duct. The thinned walls create a reliability problem for the transition duct, which renders the transition duct unusable. Consequently, the transition duct must be replaced, instead of being refurbished or repaired, which increases the maintenance cost for the gas turbine system.
Accordingly, a need exists for a new method of refurbishing a transition duct for a gas turbine system, where the method is less labor intensive, less costly, and more precise when compared to the aforementioned process.
For simplicity and clarity of illustration, the drawing figures illustrate the general manner of construction, and descriptions and details of well-known features and techniques are omitted to avoid unnecessarily obscuring the invention. Additionally, elements in the drawing figures are not necessarily drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention. Furthermore, the same reference numerals in different figures denote the same elements.
Additionally, the terms first, second, third, fourth, and the like in the description and in the claims, if any, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is further understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other sequences than illustrated or otherwise described herein.
Furthermore, the terms left, right, front, back, top, bottom, over, under, and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than illustrated or otherwise described herein.
Additionally, the terms “comprise,” “include,” “have,” and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements, but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.